1. Field of the Invention
This invention relates to a hose which can beneficially be used for transporting carbon dioxide as a refrigerant in an automobile air conditioner or the like. More particularly, it relates to a hose having an improved and reliable impermeability to carbon dioxide having a very low molecular weight as compared with flons such as Freons, even when it is subjected to high temperature and pressure.
2. Description of the Related Art
There has been a large demand for a hose having a wall not allowing the permeation of the refrigerant transported therein, and thereby overcoming various problems including the destruction of the ozone layer by Freons, or satisfying various requirements including a demand for a cooler system not calling for any replenishment of its refrigerant. The transportation of carbon dioxide as a refrigerant has, among others, been found to require an improved hose, since it has a low molecular weight and easily permeates through the wall of the hose, particularly when the hose is subjected to high temperature and pressure.
Accordingly, there has been proposed a hose having a wall composed of a plurality of layers including a rubber layer and an impermeable(or low-permeable) layer formed from a resin having a relatively high impermeability to a refrigerant, such as EVOH or nylon, or a like layer formed of a metallic foil having a high impermeability to a refrigerant. An impermeable layer formed from a resin, however, requires a considerably large thickness for the wall of a hose to resist the permeation of carbon dioxide transported as a refrigerant for a compressor in an automobile or the like. The hose is, therefore, likely to lack flexibility and have its wall cracked, or have its impermeable layer separated from a rubber layer adjoining it, due to a bending stress produced by the vibration of the compressor or the automobile.
A layer formed of a metallic foil, particularly a laminate of foils united by a fused resin film to increase the strength, is useful for making a hose having a wall of high impermeability to carbon dioxide without depriving it of flexibility. The pressure to which the hose is subjected is, however, so high that the expansion or elongation of the hose may cause the stretching of its wall resulting in the breakage of the foil. Thus, the impermeability of the wall will be seriously lowered at the critical point of breakage of the layer.